1. Field of the Invention
This invention relates generally to brake systems for wheeled motor vehicles, and more specifically it relates to a brake master cylinder and pedal feel emulator for a brake-by-wire system.
2. Background Information
Hydraulic-operated service brakes of a motor vehicle comprise a hydraulic master cylinder that is coupled via hydraulic brake lines to hydraulic wheel brakes at individual wheels. When a plunger of the master cylinder is depressed by a brake pedal to apply the wheel brakes, resistance is encountered. That resistance is typically due to a combination of the actual brake applications at the wheels and the force of a return spring acting on the pedal. Consequently, an operator of the vehicle expects to sense that resistance as a normal incident of driving.
A brake-by-wire system that utilizes a pedal to depress the master cylinder plunger performs the service brake function by selectively applying one of hydraulic brakes and brake-by-wire controlled brakes. Hydraulic brakes generally apply friction forces directly from the master cylinder to the wheels to dissipate energy as heat. Hydraulic brakes are typically used as a backup to brake-by wire controlled braking. Brake-by-wire controlled brakes generally are capable of applying friction forces to the wheels independent of the master cylinder displacement. Whether hydraulic or brake-by-wire controlled brakes are applied is determined by an electronic controller. Because flow of hydraulic fluid from the master cylinder to the wheel brakes is isolated from the friction brakes in brake-by-wire controlled braking when the controller determines that brake-by-wire controlled braking is to be applied, it may be considered desirable to associate an emulator with the master cylinder so that the feel sensed by the operator depressing the brake pedal is similar, and ideally identical, to the feel sensed when the hydraulic brakes are applied in a non-brake-by-wire braking system.
U.S. Pat. Nos. 5,729,979 and 5,927,825 disclose pedal feel emulators associated with master brake cylinders in brake-by-wire systems. Additional U.S. patents developed by a preliminary novelty search include: U.S. Pat. Nos. 4,526,003; 4,655,511; 5,253,929; 5,378,052; 5,421,643; 5,567,021; and 5,749,633.